The present invention relates to an ignition timing control system for internal combustion engines in which a knocking is detected from a vibration or a noise caused in or outside of a cylinder of an internal combustion engine by the pressure in the cylinder, and the ignition timing is retarded by a knocking signal detected.
In recent years, various investigations have been made into what is called the knocking feedback system for detecting a knocking caused in an internal combustion engine thereby to retard the ignition timing. Such a system will be described briefly. Vibrations or noises which are caused in or outside of a cylinder of an internal combustion engine by the pressure in the cylinder are detected, and when a vibration or a noise exceeds a set level (a knocking decision level), a knocking is decided, thereby generating a knocking signal. In the presence of this knocking signal, the ignition timing is retarded, while in the absence thereof, the ignition timing is advanced, so that the ignition timing is always controlled almost to the knocking limit, thus improving the fuel economy and output performance of the engine.
In this knocking feedback system, the ignition timing is retarded, upon detection of each knocking, generally by about 1.degree. cA. The amount of retardation per knocking is an important factor relating to the controllability of the ignition timing. Generally, with the decrease in the amount of retardation, the stability of ignition timing is increased, while the knocking noise increases especially in the transient period such as acceleration, thereby extremely deteriorating the operating performance under the transient conditions. If the amount of retardation is increased to some degree, on the other hand, the operating performance under the transient conditions is improved but the stability of ignition timing under normal operating conditions is deteriorated, thus deteriorating the running performance under normal operating conditions. The amount of retardation corresponding to an unsatisfactory compromise between the performance under normal operating conditions and transient conditions is actually employed, or the amount of retardation is determined by ignoring one of the two conditions (normally, the transient conditions). In this conventional system, the operating performance under the normal or transient operating conditions is unavoidably deteriorated.